Backpack



FIG. 1 is a perspective view of a backpack showing my new design;

FIG. 2 is a front view thereof;

FIG. 3 is a right side view thereof;

FIG. 4 is a left side view thereof;

FIG. 5 is a top view thereof;

FIG. 6 is a bottom view thereof; and,

FIG. 7 is a rear view thereof.

The broken lines immediately adjacent to the shaded area represent unclaimed boundaries of the design. The broken lines showing of the nine circles within the shaded region and the broken line showing of the remainder of the backpack are for environmental purposes only and form no part of the claimed design. 

The ornamental design for a backpack, as shown and described. 